Worksheetfunction.match arguments causing function to fail

I want to fill an array with found values using worksheetfunction.match and cannot find a way to make it work. I have tried multiple ways and only get 'Unable to get the Match property of the WorsheetFunction class'.

This is the loop I am using to match the values. It should not have any complications.

For i = 1 To UBound(MyConcat)
   If IsNumeric(WorksheetFunction.Match(Range("AG" & (20 + i)), Range("AN21:AN" & LastRow), 0)) = True Then
   ResultArray(arraycounter) = MyConcat(i, 1)
   arraycounter = arraycounter + 1
   Else
   End If
Next

Thanks for your help.